Parylene deposition apparatus including a heated and cooled dimer crucible

ABSTRACT

Chemical vapor deposition apparatus is provided for the quick and efficient deposition of Parylene AF4 onto silicon wafers in the production of semiconductor chips. The apparatus includes a heated and cooled dimer receptacle for fast and efficient vaporization of parylene dimer material.

BACKGROUND AND SUMMARY OF THE INVENTION

Related Applications

This application is related to the following copending commonly assignedpatent applications: Ser. No. 549,093, filed Oct. 27, 1995, and entitledPARYLENE DEPOSITION APPARATUS INCLUDING AN ATMOSPHERIC SHROUD AND INERTGAS SOURCE; Ser. No. 549,635, filed Oct. 27, 1995, and entitled PARYLENEDEPOSITION APPARATUS INCLUDING A HEATED AND COOLED SUPPORT PLATEN AND ANELECTROSTATIC CLAMPING DEVICE; Ser. No. 549,169, filed Oct. 27, 1995,and entitled PARYLENE DEPOSITION APPARATUS INCLUDING A TAPEREDDEPOSITION CHAMBER AND DUAL VACUUM OUTLET PUMPING ARRANGEMENT; Ser. No.549,087, filed Oct. 27, 1995, and entitled METHOD AND APPARATUS FOR THEDEPOSITION OF PARYLENE AF4 ONTO SEMICONDUCTOR WAFERS; Ser. No. 549,133,filed Oct. 27, 1995, and entitled PARYLENE DEPOSITION APPARATUSINCLUDING A QUARTZ CRYSTAL THICKNESS/RATE CONTROLLER; Ser. No. 549,130filed Oct. 27, 1995, and entitled PARYLENE DEPOSITION APPARATUSINCLUDING DRY VACUUM PUMP SYSTEM AND DOWNSTREAM COLD TRAP; and Ser. No.549,131, filed Oct. 27, 1995 and entitled PARYLENE DEPOSITION APPARATUSINCLUDING A POST-PYROLYSIS FILTERING CHAMBER AND A DEPOSITION CHAMBERINLET FILTER.

The instant invention relates to chemical vapor deposition (CVD)apparatus and methods, and more particularly to a parylene depositionapparatus including a heated and cooled dimer crucible.

Parylene is a general term used to describe a class of poly-p-xylyleneswhich are derived from a dimer having the structure: ##STR1## wherein Xis typically a hydrogen, or a halogen. The most commonly used forms ofparylene dimers include the following: ##STR2##

Parylene coatings are obtained from their related parylene dimers bymeans of a well-known vapor deposition process in which the dimer isvaporized, pyrolized, i.e. cleaved into a monomer vapor form, and fed toa deposition chamber wherein the monomer molecules deposit andpolymerize onto a substrate disposed within the deposition chamber. Theprocess occurs according to the following reaction: ##STR3##

Due to their ability to provide thin films and conform to substrates ofvaried geometric shapes, parylene polymers are ideally suited for use asa conformal external coating in a wide variety of fields, such as forexample, in the electronics, automotive, and medical industries.

Octafluoro- 2,2!paracyclophane (Parylene AF4 dimer) is a fluorinesubstituted version of the above-noted parylene dimers and has thestructure: ##STR4## It is known that parylene coatings which are derivedfrom the AF4 dimer by the vapor deposition process have a very highmelting temperature (about 500° C.) and a very low dielectric constant(about 2.3). These characteristics make Parylene AF4 ideally suited formany high temperature applications, including electronic applications,and potentially as an inter-layer dielectric material in the productionof semiconductor chips. The existing parylene coating systems as usedwith Parylene C, D, and N, typically include a chamber system comprisinga vaporization chamber including means for heating the powdered dimermaterial to a predetermined vaporization temperature, a pyrolysischamber coupled to the vaporization chamber, and a deposition chambercoupled to the pyrolysis chamber in which the monomer vapor depositsonto a substrate and polymerizes. The coating systems further include avacuum system coupled to the chambers for creating sub-atmosphericpressure conditions throughout the chamber system. While the existingparylene deposition systems are highly effective in depositing paryleneC, D, and N, there are unique processing constraints of semiconductorchip manufacturing which prevent the existing parylene coating systemsfrom providing sufficient speed of coating to be compatible withexisting semiconductor chip manufacturing technologies, semiconductorchip cost structures, and semiconductor chip manufacturing timeconstraints.

One aspect of fast and efficient parylene deposition is the timerequired to heat the parylene dimer to the desired vaporizationtemperature. Conventional parylene vaporization chambers, as known inthe prior art, are typically heated by an external wrap-type heatingelement, and require 10-20 minutes for the vaporization chamber to reachthe proper vaporization chamber. Although effective, conventionalsemiconductor chip manufacturing processes require faster cycle timesfor individual coatings.

Accordingly, there is currently presented a need for a parylenedeposition system particularly suited to the quick and efficientdeposition of parylene polymers onto semiconductor wafers. In thisregard, the instant invention provides a parylene deposition systemcomprising a vaporization chamber including a heated and cooled dimercrucible for the vaporization of parylene AF4 dimer. More specifically,the vaporization chamber comprises a cylindrical housing having an inletend and an outlet end. The inlet end of the housing is provided with ahinged door to permit selective access to the interior of the housingfor the placement of Parylene AF4 dimer into the vaporization chamber.Located inside the vaporization chamber is a dimer heating device whichis effective for vaporization of the dimer. The powdered AF4 dimer isreceived in a removable dimer crucible, which is in turn received into aheat transfer receptacle. The heat transfer receptacle is preferablyheated by a plurality of electric heating elements disposed around thereceptacle in intimate thermal contact with the receptacle. The electricheating elements are operative for quickly heating the receptacle to atemperature which is suitable for the vaporization of the dimer. Thedimer heating device further includes a cooling assembly for quicklycooling the heat transfer receptacle to a temperature below thevaporization temperature of the dimer. The cooling assembly comprises aheat exchange coil disposed in intimate thermal contact with the heattransfer receptacle and a heat exchange pump for circulating a coolerfluid through the heat exchange coil. The cooling assembly can beutilized to quickly cool the dimer to quench vaporization, i.e. reducethe rate of vaporization.

Accordingly, among the objects of the instant invention are: theprovision of a parylene deposition apparatus effective for quick andefficient deposition of Parylene AF4 onto silicon wafers in theproduction of semiconductor chips; the provision of a parylenedeposition apparatus including a heated and cooled dimer crucible forfast and efficient vaporization of the dimer material; and the furtherprovision of means for fast, efficient, and cost effective deposition ofParylene Af4 onto the surface of a silicon wafer.

Other objects, features and advantages of the invention shall becomeapparent as the description thereof proceeds when considered inconnection with the accompanying illustrative drawings.

DESCRIPTION OF THE DRAWINGS

In the drawings which illustrate the best mode presently contemplatedfor carrying out the present invention:

FIG. 1 is a schematic drawing of the parylene vapor deposition apparatusof the instant invention;

FIG. 2 is a front elevational view of the parylene deposition apparatusof the instant invention;

FIG. 3 is another front elevational view with the deposition chambersub-assembly separated from the base, and a portion of the base portionbroken away to illustrate the heated and cooled platen assembly of theinvention;

FIG. 4 is a cross-sectional view of the apparatus as taken along line4--4 of FIG. 3;

FIG. 4A is a cross-sectional view of the post-pyrolysis chamber as takenalong line 4A-4A of FIG. 4;

FIG. 5 is an enlarged cross-sectional view of the vaporization chamber;

FIG. 6 is another cross-sectional view of the apparatus as taken alongline 6-6 of FIG. 3;

FIG. 7 is a top view of the base illustrating the platen, and vacuumports;

FIG. 8A is a cross-sectional view of the quartz crystal thickness/ratesensor on the invention as taken along line-8A--8A of FIG. 7;

FIG. 8B is an enlarged cross-sectional view of the platen andelectrostatic clamping device of the instant invention as taken alongline 8B--8B of FIG. 7;

FIG. 9 is a schematic view of the quartz crystal thickness/rate sensorcontrol system of the invention;

FIG. 10 is a cross-sectional view of the deposition chamber body astaken along line 10--10 of FIG. 3; and

FIG. 11 is a bottom view of the deposition chamber body illustrating thedistribution of the openings in the vacuum manifold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, a parylene deposition apparatus inaccordance with the instant invention is illustrated and generallyindicated at 10 in FIGS. 1-11. As will hereinafter be more fullydescribed, the instant parylene deposition apparatus 10 is effective forthe quick and efficient deposition of Parylene AF4 material onto thesurface of a silicon wafer.

Referring to FIG. 1, the parylene deposition apparatus 10 generallycomprises a platen assembly generally indicated at 12 for supporting asemiconductor wafer 13, a vaporization chamber generally indicated at14, a pyrolysis chamber generally indicated at 16, a post-pyrolysischamber generally indicated at 18, a deposition bell generally indicatedat 20, a vacuum pump 22, and a cold trap generally indicated at 24.Referring to FIGS. 2-7, the vaporization chamber 14, pyrolysis chamber16, post-pyrolysis chamber 18, vacuum pump 22, and cold trap 24 arelocated within a rectangular housing structure as generally indicated at25 in FIGS. 2-7. The apparatus 10 further comprises an atmosphericshroud 26 which completely envelopes the entire apparatus 10, and asource of nitrogen gas 27 which is introduced into the shroud 26 by asuitable pipe assembly 28.

The platen assembly 12 is preferably located on a top wall 29 of thehousing 25 to facilitate placement and removal of the wafers 13 on theplaten assembly 12. The deposition bell 20 is received and secured overthe platen assembly 12 to form a deposition chamber. The deposition bell20 and its associated inlet and outlet pipes 30 and 32 respectively, arepreferably formed as a single removable unit (See FIG. 3), and arearranged so as to provide a mating engagement of the deposition bell 20with the top of the platen assembly 12 and a mating engagement of theinlet and outlet pipes 30, 32 with corresponding fittings on the topwall 29 of the housing 25. The removable deposition bell 20 furtherfacilitates access to the platen assembly 12 for the placement andremoval of wafers 13. While there is shown and described a specificarrangement of the platen assembly 12 and removable deposition bell 20,it is to be understood that other arrangements are also within the scopeof the invention.

Referring to FIGS. 3, 7 and 8B, the platen assembly 12 comprises athermally conductive platen generally indicated at 34 having asupporting surface 36 for supporting a wafer 13 to be coated, aplurality of electric heater elements 38 for heating the platen 34 to apredetermined temperature, and a cooling sub-assembly 40 for cooling theplaten 34 to a predetermined temperature. It has been found thatParylene AF4 vapor condenses or polymerizes most effectively on surfaceswhich have been chilled to a temperature of below 0° C. The platen 34 ofthe instant invention provides an effective surface 36 for supporting asemiconductor wafer 13 within the deposition bell 20, and furtherprovides an effective means for heating and cooling the wafer 13 todesired temperatures during the coating process. More specifically, theheating and cooling of a wafer 12 is accomplished by means of heatconduction through contact with the platen 34. The platen 34 ispreferably constructed from a metallic material which has very goodthermal conduction characteristics. In this regard, brass and copper aresuitable metallic materials for construction of the platen 34. Theheating elements 38 for heating the platen 34 comprise electriccartridge heating elements which are inserted into radially extendingopenings 42 formed in a body portion of the platen 34 (See FIG. 3). Thecooling sub-assembly 40 comprises a heat exchange coil 44 disposed inintimate thermal contact with the body portion of the platen 34, andfurther comprises a heat exchange pump 46 effective for circulating achilled fluid through the heat exchange coil 44. The specifics of heatexchange coil construction and heat exchange pumps are well known in theheat transfer arts, and therefore, they will not be described furtherherein. In operation, the chilled fluid is circulated through the heatexchange coil 44 to lower the temperature of the wafer 13 on the surface35 of the platen 34 to a desired temperature. Once the wafer 13 is atthe desired temperature, the deposition process can proceed. However,since the wafer 13 is now chilled, i.e. cooler than room temperature,the wafer 13 cannot thereafter be immediately removed from thedeposition chamber because moisture from the air will condense on thechilled wafer. In this connection, the heating elements 38 are effectivefor quickly heating the wafer 13, i.e. raising the temperature of theplaten back to room temperature, before removal of the wafer 13 from thedeposition chamber. This procedure will effectively eliminate anychances of condensation forming on the wafers. It is also contemplatedthat the heating elements 38 may be effective for further raising thetemperature of the wafer 13 up to a temperature of 100° C. to 400° C.for purposes of annealing the Parylene coating after deposition.

Referring to FIGS. 7 and 8B, the platen assembly 12 further comprises anelectrostatic clamping device generally indicated at 48 forelectrostatically clamping the semiconductor wafer 13 in intimatethermal contact with the platen surface 36. Since the wafer temperatureis controlled primarily by means of heat conduction from the platen 34,it is important to maintain an intimate thermal contact of the wafer 13with the platen surface 36. The electrostatic clamping device 48provides an extremely simple way of maintaining an intimate thermalcontact without cumbersome mechanical clamping devices. Theelectrostatic clamping device 48 is located on the surface 36 of theplaten 34, and comprises an inter-digital printed circuit capacitor 50sandwiched between two layers of a thermally conductive, dielectricmaterial 52, 54 respectively. The circuit capacitor 50 is energized by aconventional electric source (not shown) having leads 56 insulated at 58which pass through the platen 34 and connect to the capacitor 50 asindicated in FIG. 8B. The specific details of a representative-typeelectrostatic clamping device 48 are described in U.S. Pat. No.4,184,188, the content of which is incorporated by reference herein.

Referring to FIGS. 1, 4 and 5, the vaporization chamber 14 comprises acylindrical housing generally indicated at 60 having an inlet end 62 andan outlet end 64. The inlet end 62 of the housing 60 is provided with ahinged door 66 which is attached to a flange 68 of the housing 60. Thehinged door 66 is movable between open and closed positions to permitselective access to the interior of the housing 60 for the placement ofParylene AF4 dimer 69 into the vaporization chamber 14. In order tomaintain a vacuum seal at the door opening, the door 66 is provided withan elastomeric gasket 70. Located inside the vaporization chamber 14 isa dimer heating device generally indicated at 72 which is effective forvaporization of the dimer 69. The powdered AF4 dimer 69 is received in aremovable dimer crucible 74, which is in turn received into a heattransfer receptacle 76. Alternatively, the dimer 69 may be receiveddirectly into the receptacle 76. The dimer crucible 74 and receptacle 76are preferably fashioned from a thermally conductive metal, and thedimer crucible 74 is preferably dimensioned so as to fit into thereceptacle 76 in intimate thermal contact with the receptacle 76 suchthat heat from the receptacle 76 is readily conducted to the dimercrucible 74 through contact. The heat transfer receptacle 76 ispreferably heated by a plurality of electric heating elements 78disposed around the receptacle 76 in intimate thermal contact with thereceptacle 76. The electric heating elements 78 comprise a nichrome wireconstruction, suitably insulated, and wrapped around the receptacle. Theelectric heating elements 78 are operative for quickly heating thereceptacle 76 to a temperature which is suitable for the vaporization ofthe dimer 69, which temperature is between about 70° C. and about 150°C. It can therefore be seen that the dimer heating device 72 of theinstant invention provides for quick and efficient heating of the dimer69 to the required vaporization temperature.

The dimer heating device 72 further includes a cooling assembly forquickly cooling the heat transfer receptacle 76 to a temperature belowthe vaporization temperature of the dimer 69. The cooling assemblycomprises a heat exchange coil 80 (FIG. 5) disposed in intimate thermalcontact with the heat transfer receptacle 76 and a heat exchange pump 82(FIGS. 1 and 4) for circulating a cooler fluid through the heat exchangecoil 80. The specifics of heat exchange coil construction and heatexchange pumps are well known in the heat transfer arts, and therefore,they will not be described further herein. In order to effectivelycontrol rates of deposition of the Parylene AF4 onto the wafer 13, it isnecessary to control the rate of vaporization of the dimer 69 into thedeposition system. In this connection, the cooling assembly can beutilized to quickly cool the dimer to quench vaporization, i.e. reducethe rate of vaporization. Ideally, the circulating fluid would bemaintained at a temperature only slightly below the vaporizationtemperature, such that temperature of the heat transfer receptacle 76would only drop to a point effective to stop vaporization. The resultingtemperature drop may only be that of several degrees. Accordingly, itcan be seen that the heating and cooling mechanisms permit thetemperature of the heat transfer receptacle 76 to be quickly cycledabove and below the vaporization temperature to effectively control therate of vaporization of the dimer.

The outlet end 64 of the vaporization chamber 14 is coupled to an inletopening 84 of the pyrolysis chamber by a pipe 86. The pipe 86 extendingbetween the vaporization chamber 14 and the pyrolysis chamber 16preferably includes a throttle valve 88 for controlling the flow ofvaporized dimer into the pyrolysis chamber 16. In coating operations, ithas been found effective to utilize a throttle valve 88 to immediatelystop the flow of vaporized dimer into the pyrolysis chamber 16 to stopthe deposition process. In use, when it is desired to stop the coatingprocess, i.e. when a desired coating thickness has been achieved, thethrottle valve 88 is closed to prevent any further vapor flow throughthe system. The coated article can then be removed from the depositionchamber and replaced with another article to be coated. In thisconnection, when the throttle valve 88 is closed to stop flow, it isdesirable to stop further vaporization of the dimer 69 within thevaporization chamber 14 as further vaporization will increase pressurewithin the vaporization chamber 14 and cause a rush of vapor into thesystem when the throttle valve 88 is reopened. Accordingly, the coolingassembly would be employed to quickly cool the dimer and quenchvaporization.

The pyrolysis chamber 16 receives the vaporized dimer from thevaporization chamber 14, and is effective for super-heating thevaporized dimer to a predetermined pyrolysis temperature wherein thedimer is cleaved into monomer form. The construction of pyrolysischamber 16 is conventional in the art comprising a tube 90 (brokenlines), the walls of which are heated by an electric tube heater 92. Thetube heater 92 is preferably effective for maintaining the pyrolysischamber 16 at a temperature of about between about 600° C. and about720° C., and more preferably at a temperature of about 690° C.

The outlet of the pyrolysis chamber 16 is coupled to an inlet of thepost-pyrolysis chamber 18. The post pyrolysis chamber 18 comprises acylindrical housing 94 having a plurality of baffle elements 96 disposedin the interior thereof. The monomer exiting from the pyrolysis chamber16 passes through the post-pyrolysis chamber 18 on its way to thedeposition chamber 20, wherein the post-pyrolysis chamber 18 iseffective for capturing any unpyrolyzed dimer that may pass through thepyrolysis chamber 16. More specifically, the post-pyrolysis chamber 18is maintained at a temperature of between about 22° C. and about 28° C.,and more preferably at a temperature of about 25° C. (about roomtemperature). The post-pyrolysis chamber is maintained at its desiredtemperature by means of an external fan 98. With regard to capturing ofthe unpyrolyzed dimer, it has been found that the unpyrolyzed dimer,being twice as heavy as the reactive monomer, preferentially condenses,or deposits, in the post-pyrolysis chamber 18 when the post-pyrolysischamber 18 is maintained at the indicated temperatures. Removal of theunpyrolyzed dimer before deposition is important in the coating ofsemiconductor wafers, as the unpyrolyzed dimer constitutes an impurityin the polymer chain which may locally effect dielectric constant andpolymer surface characteristics.

The outlet of the post-pyrolysis chamber terminates in a fitting 100located on the top wall 29 of the housing 25, and is coupled to theinlet pipe 30 of the deposition bell 20. In this regard, the inlet pipe30 includes a complimentary fitting 102 which is received in matingengagement with the fitting 100 when the deposition bell 20 is receivedonto the platen 34. The fittings 100, 102 are provided with anelastomeric gasket 104 to provide a vacuum tight engagement.

Referring to FIGS. 2, 3, 10 and 11, the deposition bell 20 isfrusto-conical in shape having a smaller diameter inlet end and a largerdiameter outlet end. The outlet end of the deposition bell 20 is definedby a rim 106 which is received in mating engagement with the supportingsurface 36 of the platen 34 to define a fursto-conical shaped depositionchamber. The particular shape of the deposition bell 20 minimizesdeposition chamber volume and maximizes vapor flow over the surface ofthe wafer 13 supported on the platen 34 adjacent to the outlet end ofthe chamber. While the bell 20 is illustrated as being fursto-conical,it is to be understood that virtually any tapered arrangement of thebell 20, such as a pyrimidal shape, would provide the desiredminimization of volume and, and maximization of vapor flow. Thedeposition bell 20 further includes a filter assembly generallyindicated at 108 disposed adjacent to the inlet end thereof forfiltering out impurities in the vapor. The filter assembly is positionedin the interior of the bell 20 and comprises a filter element 110captured between two opposing annular rings 112, 114 respectivelysecured to the interior wall of the bell 20 with appropriate removablefasteners, such as screws. The filter element 110 preferably comprises amicroscopic filter material, such as PTFE, which permits sufficient gasflow and which is capable of filtering substantially all airborneimpurities having a size larger than 0.1 micron. It is noted that thelower ring 114 is easily removable for periodic replacement of thefilter element 110.

In order to draw a vacuum flow through the deposition bell 20 from theinlet end to the outlet end, the vacuum pump 22 is coupled to aplurality of outlets 116 in the rim 106 by means of a distributionmanifold 118. The distribution manifold 118 comprises and annularchannel which is secured to the outer surface of the rim 106. The outletopenings 116 communicate with an interior channel 120 of the manifold118. A first, smaller diameter, outlet pipe 122 is connected to themanifold 118 in a predetermined location, and the plurality of outletopenings 116 are distributed around the periphery of the rim 106 in adistribution pattern intended to equalize the vacuum flow throughout thechamber. More specifically, it can be seen in FIG. 11, that there aremore outlet openings 116 further away from the connection point of theoutlet pipe 122 than adjacent to the outlet pipe 122. In other words,the cross-sectional flow area are the openings 116 increases further andfurther away from the vacuum source 122.

While the described vacuum flow/manifold arrangement is ideal fordrawing a uniform vapor flow over the surface of the wafer 13 during thedeposition process, i.e. maintaining an operating vacuum pressure withinthe chamber system, the cross-sectional flow area of the first outletpipe 122 is not sufficient to provide a quick evacuation of the chambersystem down to the operating pressure. In other words, a significantamount of time is required to pump down the chamber system to theoperating pressure utilizing the first outlet pipe 122 by itself.Accordingly, in order to reduce the vacuum cycle time, the depositionbell 20 is provided with a vacuum by-pass arrangement illustrated inFIGS. 2 and 3. In this regard, the inlet of the deposition bell 20 isconnected to a second, larger diameter outlet pipe 32, which is providedwith a by-pass valve 124 adjacent the deposition bell inlet. The smallerdiameter outlet pipe 122 merges with the larger diameter outlet pipe 32at fitting 126, and the outlet pipe 32 is coupled to the vacuum pump 22.More specifically, the outlet pipe 32 terminates in a fitting 128 whichengages with a vacuum fitting 130 on the top wall 29 of the housing 25.The fitting 130 is coupled to the vacuum pump 22 by another pipe section132 (FIG. 6). The outlet pipe fitting 128 is received in matingengagement with housing fitting 130 when the deposition bell 20 isreceived on the platen 34. The fittings 128, 130 are provided with anelastomeric gasket 134 to maintain a vacuum tight engagement. Inoperation, by-pass valve 124 would remain open, wherein initialpump-down of the chamber system would be accomplished through both thefirst and second outlet pipes 122, and 32. As soon as a desiredoperating pressure is achieved, the by-pass valve 124 is closed, and thedesired pressure is maintained solely by the first outlet pipe 122connected to the distribution manifold 118.

Referring to FIG. 6, the pipe section 132 is coupled to the inlet of thevacuum pump 22, and is preferably provided with a valve 136 forselectively providing a vacuum to the chamber system. The valve 136 islocated downstream of the fitting 130 so that the deposition bellassembly 20 can be removed from the top of the housing 25 when the valve136 is closed. The vacuum pump 22 comprises an oil free, or dry, vacuumpump, such as a DRYTEL SERIES dry pump manufactured by ALCATEL, Inc. Theoutlet of the vacuum pump 22 is coupled to an inlet of the cold trap 24which comprises a cylindrical tube 138 having an open top. The tube 138is mounted to the top wall 29 of the housing 25 and includes a fitting140 at the open top thereof. A cylindrical finger element 142 having acomplementary flange 144 at the top thereof is slidably received intothe tube 138 with the fittings 138, 140 engaging at the top. Thefittings 138, 140 are provided with an elastomeric gasket 142 for avacuum tight engagement. The finger element 142 is preferably cooled bymeans of liquid nitrogen received in a cylindrical opening in the top ofthe finger element 142. The outlet of the cold trap 24 opens to ambientatmosphere by means of a pipe 146. In operation, any free monomer whichdid not deposit in the deposition chamber deposits onto the surface ofthe cold finger 142 disposed in the cold trap chamber.

The use of an oil-free, dry pump is significant in terms of its use witha Parylene AF4 deposition apparatus. The prior art parylene depositiondevice typically utilized a cold trap directly connected to thedeposition chamber outlet, and a conventional vacuum pump downstream ofthe cold trap. The primary purpose of placing the cold trap between thedeposition chamber and the vacuum pump was to trap any excess monomerand prevent the monomer from flowing through the pump where it coulddeposit internally and interfere with operation of the pump and/orcontaminate the oil. The prior Parylene materials (Parylene C, D, and N)effectively deposited onto surfaces having a temperature of about15°-40° C. which just happens to be the normal operating temperatures ofsuch pumps. The cold trap was further effective for preventingback-streaming of oil vapors into the deposition chamber. Hence, thecold trap was necessary to trap excess monomer from depositing onto theinternal surfaces of the vacuum pump, and prevent oil vapor fromback-streaming into the deposition chamber.

However, placement of the cold trap in direct communication with thedeposition chamber is known to cause at least one drawback. It has beenfound that the cold trap creates a cryo-pumping arrangement which hasbeen shown to rapidly draw monomer through the system faster than thebackground atmosphere is pumped by the vacuum pump. The result is thatthe monomer is drawn very quickly through the deposition chamber, and isnot allowed sufficient time to polymerize. The problem has beencompensated for by utilizing excess dimer, and increasing coating cycletime. This was not previously found to be that significant a drawback inthat the cost of Parylene C, D, and N is not prohibitive.

It has been found that the newer parylene AF4 will not deposit ontoheated substrates in the range of 15°-40° C., and thus the prior problemof pump deposition is eliminated. However, the use of an oil pump stillleaves the problem of oil vapor back-streaming into the depositionchamber. Since one of the intended uses of the apparatus 10 is in thecoating of highly sensitive semiconductor wafers, the presence of anyforeign vapors is not desired. The instant arrangement of an oil-freevacuum pump effectively eliminates the need for an upstream cold trap,and eliminates the stated drawbacks of the prior art devices.Furthermore, since the vacuum pump is connected directly to thedeposition chamber outlet, both the background gasses and the monomervapor are drawn at an equal rate through the deposition chamber, thusreducing the amount of dimer needed to effectuate the desired coatingthickness. This is highly significant when considered in conjunctionwith the high cost of Parylene AF4 dimer, and the desire the reduce thequantity utilized for each deposition cycle.

Referring to FIG. 1, the parylene deposition apparatus further comprisesan electronic controller generally indicated at 148 operative forelectronically controlling all aspects of the deposition process,including temperature, and pressure regulation. The controller 148comprises a conventional microprocessor device 150 which is programmedaccording to conventional programming techniques well known in theelectronics arts. With regard to temperature regulation, the heating andcooling devices of the vaporization chamber 14, pyrolysis chamber 16,post-pyrolysis chamber 18, and platen assembly 12 are each connected tothe controller 148 by appropriate electrical connections. Furthermore,the vaporization chamber 14, pyrolysis chamber 16, post-pyrolysischamber 18, and platen assembly 12 are each provided thermocouples 152,154, 156, 158 respectively, or other appropriate device for measuringtemperature. The thermocouples 152, 154, 156, 158 are connected to thecontroller 148 by appropriate electrical connections wherein the desiredtemperatures of the various chambers are monitored by various set pointcomparators 160, and wherein the heating and cooling devices arecontrolled by the controller 148 responsive to the measured temperaturesto maintain the desired set point temperatures. With regard to pressureregulation, the vacuum pump 22 and associated valves 124, 136 areconnected to the controller 148 for automated control of the vacuumsystem. The deposition bell 20 is provided with a thermistor gauge 162for measuring pressure within the deposition chamber, and the thermistorgage 162 is connected to the controller 148 wherein the vacuum pump 22and valves 124, 136 are controlled responsive to measured pressure.Furthermore, the throttle valve 88 adjacent the vaporization chamber 14is also connected to the controller 148 for automated control of thevalve 88, and the electrostatic clamping device 48 is connected to thecontroller 148 for automated control of the clamping device 48.

Referring to FIGS. 1, 7, 8A, and 9, the instant parylene depositionapparatus still further includes a quartz-crystal thickness/vaporizationrate control system including a quartz crystal assembly generallyindicated at 164 disposed within the deposition chamber. Morespecifically, the quartz crystal assembly 164 is disposed within arecess 166 located on the peripheral edge of the platen 34. The crystalassembly 164 includes a disc-shaped crystal 168 and two electrical leads170, 172 mounted to opposing sides of the crystal 168. In operation, theparylene monomer vapor deposits onto the surface of the crystal 168varying the vibration frequency of the crystal 168. The rate of changein frequency can be directly correlated with rate of deposition of theparylene monomer onto the crystal 168, and thus onto the substrate to becoated. The crystal 168 is electrically connected to an oscillator 174for measuring the frequency of the crystal 168 which varies with thethickness of the coating on the crystal 168. The oscillator 174 isconnected to the micro-controller 148 which measures the frequencychanges of the crystal and continuously calculates the rate ofdeposition of the parylene monomer vapor. Furthermore, themicroprocessor 150 is connected to a set point comparator 160 whichcompares the calculated deposition rate to a set or desired depositionrate. The microprocessor 150 then operates to increase or decrease thetemperature of the vaporization chamber 14, or to open or close thethrottle valve 88 to provide more or less parylene dimer to the system.In other words, the controller 148 monitors the changes in frequency ofthe crystal 168 as parylene is deposited onto the crystal 168, andadjusts the amount of parylene dimer released into the system byadjusting the temperature of the vaporization chamber 14, andcontrolling the throttle valve 88. The oscillator 174 and set pointcomparator 160 are well known items in the electronics arts, andtherefore they will not be described further.

A primary consideration in development of the instant apparatus is theextremely high cost of Parylene AF4 materials. In order to make ParyleneAF4 coatings cost efficient, it is important that deposition efficiencybe relatively high. Since Parylene AF4 has an affinity to deposit ononly cool substrates, it is desirable to heat the internal walls ofseveral areas of the apparatus 10 to prevent the dimer and monomer fromdepositing onto the internal walls of the apparatus. More specifically,the internal walls of the vaporization chamber 14 are provided withindependent heating elements 176 to prevent the vaporized dimer fromdepositing onto the walls of the chamber 14 after vaporization.Furthermore, the door 66 of the vaporization chamber 14 is provided witha heating element 178 to prevent deposition onto the inside surface ofthe door 66. The walls of the deposition bell 20 are also provided withheating elements 180 to prevent the monomer from depositing onto theinternal walls of the deposition chamber. In this connection, the wallsof the deposition bell 20 should be heated to a temperature of betweenabout 30° and about 50° C. to effectively prevent deposition. Stillfurther, the by-pass valve 124 adjacent the inlet of the deposition bell20 is provided with a heating element 182 to prevent the monomer fromdepositing onto the valve surface before reaching the depositionchamber.

As described hereinabove, the entire apparatus 10 is enveloped in anatmospheric shroud 26, and provided with an inert nitrogen atmosphere.The purpose of the shroud 26 and nitrogen atmosphere is to excludeoxygen from the deposition chamber during evacuation and subsequentcoating cycle, thus allowing the coating process to be carried out in anoxygen free environment. Currently, the prior art parylene coatingdevices operate in normal atmospheric conditions. This allows for oxygento be present as a constituent background gas, and as a constituent ofany atmospheric leakage into the chamber during the coating cycle. Ithas been found that oxygen can chemically combine with the Parylenereactive monomer in the pyrolysis and post pyrolysis zones 16, 18respectively, and thereby cause weak polymer bonds. Accordingly, theshroud 26 is effective to isolate the apparatus 10 in an inert nitrogenatmosphere before pump down, and during the coating cycle. Preliminarytest results have shown that the inert atmosphere provides a purer,denser and more stable coating. While nitrogen is specifically describedherein as the preferred atmospheric element, it is to be understood thatother inert gases, such as argon, are also suitable for the intendedpurpose.

A representative use of the apparatus 10 will be described by way of thefollowing example wherein an 8 inch silicon wafer 13 will be coated witha 1 micron layer of Parylene AF4. With the vacuum control valve 136closed, the deposition bell assembly 20 is removed and the wafer 13placed in the center of the platen 34. The electrostatic clamp 48 isactivated to hold the wafer 13 in position, and the deposition bell 20is replaced. Prior to evacuation of the chambers, about 1 gram ofParylene AF4 dimer is placed into the dimer crucible 74, and thecrucible 74 placed in the heat transfer receptacle 76 in thevaporization chamber 14. The shroud 26 is then flooded with nitrogen toprovide an inert atmosphere around the apparatus 10. The vacuum controlvalve 135 and vacuum by-pass valve 124 are both opened to beginevacuation of the chamber systems. Chamber pressure is preferablyreduced to about 5 microns mercury (Hg), after which the by-pass valve124 is closed. The pressure is thereafter maintained at 5 microns Hg byonly the smaller vacuum manifold outlets 116/122. The heat transferreceptacle 76 is then heated to a temperature of about 90° C. to beginvaporization of the dimer 69. The pyrolysis chamber 16 is preheated toabout 690° C., and when the vaporized dimer passes through the pyrolysischamber 16, substantially all of the dimer is pyrolyzed into monomerform and passes out through the post-pyrolysis chamber 18. Thepost-pyrolysis chamber 18, which is maintained at a temperature of about25° C. (about room temperature), captures any unpyrolyzed dimer whichmanages to escape the pyrolysis chamber 16. The AF4 monomer vapor isdrawn into the deposition chamber 20, over the surface of the wafer 13,and outward through the distribution manifold 118 wherein the monomervapor deposits onto the cooled wafer 13. As stated previously, the wallsof the deposition bell 20 are heated to prevent deposition onto thechamber walls. Vaporization of the entire gram of dimer should result inabout a 1 micron layer of Parylene AF4 of the wafer 13. However, thequartz crystal control 164 monitors the coating thickness and controlsvaporization of the dimer to achieve the desired 1 micron coatingthickness. Any excess un-deposited monomer drawn through the manifoldoutlet 122 is captured in the cold trap 124. After the desired thicknessof coating is achieved, the throttle valve 88 is closed to prevent anyfurther deposition. While maintaining the vacuum, the temperature of thewafer 13 is then brought up to room temperature by activating the platenheating elements 38. Once the wafer 13 is at the desired roomtemperature, the vacuum valve 136 is closed, the deposition bell 20removed, the electrostatic clamp 48 deactivated, and the wafer 13removed from the platen 34.

It can therefore be seen that the instant invention provides a uniqueand effective parylene deposition apparatus 10 which is uniquely suitedfor the deposition of Parylene AF4. The heated and cooled platen 34provide an effective means for supporting a wafer 13 for deposition andfor controlling the temperature of the silicon wafer 13 duringprocessing. The electrostatic clamping device 48 provides an effectivemeans for clamping the wafer in intimate thermal contact with the platen34 without physically clamping the delicate wafer structure. Thevaporization chamber 14 is effective for the quick and efficient heatingand cooling of the dimer to effectively control the dimer vaporizationrate, and the associated throttle valve 88 effective for the controlledrelease of vaporized dimer into the deposition system. The baffledpost-pyrolysis chamber 18 is effective for capturing dimer which exitsthe pyrolysis chamber. The dome-shaped deposition bell 20 is unique andeffective for minimizing deposition chamber volume while maximizingvapor flow over the surface of the platen 34. The vacuum manifoldarrangement 118 attached to the deposition bell 20 enhances vapor flowdirectly over the surface of the platen 34 and the vacuum by-passarrangement facilitates quick and efficient pump-down of the chambersystem in preparation for deposition. The quart crystal rate controller164 also provides an effective means for accurately controllingdeposition rate onto the wafers. For these reasons, the instantinvention is believed to represent a significant advancement in the art.

While there is shown and described herein certain specific structureembodying the invention, it will be manifest to those skilled in the artthat various modifications of the parts may be made without departingfrom the spirit and scope of the inventive concept and that the same isnot limited to the particular forms herein shown and described exceptinsofar as indicated by the scope of the appended claims.

We claim:
 1. A deposition apparatus comprising:a vaporization chamber; athermally conductive heat transfer receptacle disposed in saidvaporization chamber; a first heater capable of heating said heattransfer receptacle to a predetermined temperature; a second heatercapable of heating inner walls of said vaporization chamber; a pyrolysischamber coupled to said vaporization chamber; a deposition chambercoupled to said pyrolysis chamber; a platen disposed within thedeposition chamber; and a device for heating and cooling the platen. 2.The deposition apparatus of claim 1, wherein said first heater comprisesa heating element disposed in intimate thermal contact with said heattransfer receptacle.
 3. The deposition apparatus according to claim 2,further comprising a throttle valve disposed between said vaporizationchamber and said pyrolysis chamber, said throttle valve being capable ofcontrolling a gas flow between said vaporization chamber and saiddeposition chamber.
 4. The deposition apparatus of claim 1, furthercomprising a cooling device capable of cooling said heat transferreceptacle to a temperature below said predetermined temperature.
 5. Thedeposition apparatus of claim 4, wherein said cooling device comprises aheat exchange coil disposed in intimate thermal contact with said heattransfer receptacle.
 6. The deposition apparatus of claim 4, whereinsaid first heater comprises a heating element disposed in intimatethermal contact with said heat transfer receptacle.
 7. The depositionapparatus according to claim 6, further comprising a throttle valvedisposed between said vaporization chamber and said pyrolysis chamber,said throttle valve being capable of controlling a gas flow between saidvaporization chamber and said deposition chamber.
 8. The depositionapparatus according to claim 1, further comprising a throttle valvedisposed between said vaporization chamber and said pyrolysis chamber,said throttle valve being capable of controlling a gas flow between saidvaporization chamber and said deposition chamber.
 9. The depositionapparatus of claim 8, wherein said first heater comprises a heatingelement disposed in intimate thermal contact with said heat transferreceptacle.
 10. The deposition apparatus of claim 8, further comprisinga cooling device capable of cooling said heat transfer receptacle to atemperature below said predetermined temperature.
 11. A vaporizationchamber, comprising:a housing; a thermally conductive heat transferreceptacle disposed in said housing; a first heater capable of heatingsaid heat transfer receptacle to a predetermined temperature; a secondheater capable of heating inner walls of said housing; a depositionchamber in fluid communication with the housing; a platen disposedwithin the deposition chamber; and a device for heating and cooling theplaten.
 12. The vaporization chamber of claim 11, wherein said firstheater comprises a heating element disposed in intimate thermal contactwith said heat transfer receptacle.
 13. The vaporization chamberaccording to claim 12, further comprising a throttle valve disposedbetween said housing and said deposition chamber, said throttle valvebeing capable of controlling a gas flow between said housing and saiddeposition chamber.
 14. The vaporization chamber of claim 11, furthercomprising a cooling device capable of cooling said heat transferreceptacle to a temperature below said predetermined temperature. 15.The vaporization chamber of claim 14, wherein said cooling devicecomprises a heat exchange coil disposed in intimate thermal contact withsaid heat transfer receptacle.
 16. The vaporization chamber of claim 14,wherein said first heater comprises a heating element disposed inintimate thermal contact with said heat transfer receptacle.
 17. Thevaporization chamber according to claim 16, further comprising athrottle valve disposed between said housing and said depositionchamber, said throttle valve being capable of controlling a gas flowbetween said housing and said deposition chamber.
 18. The vaporizationchamber according to claim 11, further comprising a throttle valvedisposed between said housing and said deposition chamber, said throttlevalve being capable of controlling a gas flow between said housing andsaid deposition chamber.
 19. The vaporization chamber depositionapparatus of claim 18, wherein said first heater comprises a heatingelement disposed in intimate thermal contact with said heat transferreceptacle.
 20. The vaporization chamber deposition apparatus of claim18, further comprising a cooling device capable of cooling said heattransfer receptacle to a temperature below said predeterminedtemperature.